The present invention relates to a particulated, solvent free, platinum group metal silicone resin containing catalyst. More particularly, the present invention relates to the spray drying of a mixture of an organic solvent solution of an alkenyl substituted organosiloxane resin, and a solution of a platinum group metal complex.
Heat curable platinum group metal catalyzed organopolysiloxane compositions are often classified as one package or two package mixtures. A one package organopolysiloxane mixture is generally stable at ambient conditions for a period of at least several months. It is generally activated thermally or with radiant energy. A two package mixture generally cures at ambient temperatures, or at an elevated temperature within a relatively short period of time upon adding a curing catalyst to a silicone network mixture. Upon addition, of the catalyst, the resulting curable mixture should have a satisfactory "pot life" or "work life".
Although platinum group metal catalysts used in one part and two part silicone mixtures can provide valuable thin section or deep section cured silicone products, a platinum group metal catalyst, such as a platinum catalyst, is often used in the form of an organic solvent solution as shown by Lewis, U.S. Pat. No. 4,681,963. The most active platinum catalyst has been found to be zero valent platinum olefin complexes in a liquid media. However, some of these zero valent platinum catalysts suffer from poor shelf stability at ambient temperatures.
Schlak et al, U.S. Pat. No. 4,481,341, shows that a platinum catalyst also can be used as a dispersion in a solid silicone resin. Shimizu et al, U.S. Pat. No. 5,064,924, describes one part organopolysiloxane compositions which use a platinum catalyst encapsulated within finely divided particles of cured silicone rubber. In addition, the "solid encapsulated platinum catalysts", often have poor solubility in silicones.
A principal advantage of the encapsulated platinum group metal catalysts of the prior art is that these catalysts are often solvent free. However, when incorporated into a silicone to form a one or two package silicone mixture, encapsulated platinum group metal catalysts often must be activated by excessive heat to provide a satisfactory rate of cure, because the platinum group metal catalyst may be shielded by a wall of silicone.
It would be desirable therefore, to provide a solvent free, platinum group metal silicone resin containing catalyst which is both catalytically active, and has an indefinite shelf stability at ambient temperatures. It also would be advantageous to provide curable organopolysiloxane compositions having a satisfactory pot life at ambient temperatures which are catalyzed by the use of a solvent free platinum group metal catalyst.